1. Field of the Invention
This invention relates to ion implanters for preparing semiconductor lamina, and, in particular, ion implanters used for economical production of photovoltaic cells.
2. Background Information
As the demand for electrical energy based on renewable sources increases, the implementation of photovoltaic technology has expanded dramatically in recent years. Nevertheless, a way of forming crystalline silicon bodies optimized for photovoltaic cells has remained elusive.
Crystalline silicon wafers adapted to bear photovoltaic cells are conventionally obtained by slicing a silicon ingot. This process, which typically yields a silicon wafer thicker than 150 μm, wastes a substantial amount of silicon by consuming up to 50% of the silicon body in kerf loss and delivering a much greater thickness than is needed for useful photovoltaic devices.
Thinner silicon laminae have been made by exfoliation of a film by annealing after high-dose ion implantation. The films produced this way have found application in forming silicon-on-insulator structures but are cost-prohibitive for solar cells. Also, at thicknesses well under 1 μm, the films may be so thin as to make efficient light-capturing difficult. Boosting the energy of ion implant could increase the film thickness, but this adaptation would make the films even more expensive and less economical for photovoltaics.
There is, accordingly, a need for a cost-effective way to form silicon bodies optimized for photovoltaic applications.